Earthquake-triggered lightning?

Physicists offer a possible explanation for the rare claim of earthquake “lights”

People typically associate lightning with storm clouds, as shown here. But in some rare instances, earthquakes appear to generate the same electrical discharge. The big difference: That lightning can occur despite a clear sky, one free of any clouds.

DENVER — Beads and flour might help explain a rare and mysterious phenomenon: a type of lightning known as earthquake lights. People have sometimes claimed to witness them before or during major earthquakes. New results presented here on March 6 at an American Physical Society meeting showed that shifting grains of some materials can induce remarkably high electrical voltages. The same principle, on a larger scale, may occur when soil particles shift during earthquakes, they now report.

In the new experiment, Troy Shinbrot of Rutgers University in Piscataway, N.J., and his co-workers used glass and plastic beads to simulate rock and soil particles along an earthquake fault.

This study picks up on a simple experiment Shinbrot developed almost 2 years ago. He had wanted to study whether Earth under stress might create conditions favorable for lightning above the surface. So he tipped over a container of flour. And as the grains of flour poured out, a sensor inside the powder registered an electrical signal of roughly 100 volts.

For the new experiments, Shinbrot’s group put tanks of beads under pressure until one section slipped relative to another. It was meant to simulate the failing slabs of earth along a fault. Here, again, they measured a surge in voltage during each slip. The findings strengthen the idea that such a slipping phenomenon could trigger earthquake lights.

The effect seems similar to static electricity. That shouldn’t, however, build up between particles of the same material. “It’s all very curious,” Shinbrot said. “It seems to us to be new physics.”

Power Words

earthquake A sudden and violent shaking of the ground, sometimes causing great destruction, as a result of movements within Earth’s crust or of volcanic action.

fault In geology, an area where a crack in large rock formations allows one side to move relative to another when acted upon by the forces of plate tectonics.

lightning A flash of light triggered by the discharge of electricity that occurs between clouds or between a cloud and something on Earth’s surface. The electrical current can cause a flash heating of the air, which can create a sharp crack of thunder.

physics The scientific study of the nature and properties of matter and energy.

plate tectonics The study of massive moving pieces that make up Earth’s outer layer, which is called the lithosphere, and the processes that cause those rock masses to rise from inside Earth, travel along its surface, and sink back down.

simulate To imitate the form or function of something.

voltage A force associated with an electric current that is measured in units known as volts. Power companies use high-voltage to move electric power over long distances.